The present invention relates to a scramble codec which can be used for securing information such as television signals which are transmitted by transmission systems that can be easily tapped by others or information such as that photographed with a video camera which must be secured from disclosure to others. More particularly, the invention relates to a video recorder which includes a scramble codec.
The recent development of various communication media and new recording media such as optical disks has made it feasible to transmit data and information with a remarkably expanded coverage and at amazing speeds. On the other hand, the same technology has made it an easy chore to tap such data communications systems, making it increasingly difficult to insure the privacy of information. By way of illustration, it is by now the order of the day that corporate proprietary information is transmitted via. communication satellites, data including confidential business information are communicated by way of video conferences, or the data generated in experiments performed in private laboratories are recorded on the video type recorder (hereinafter abbreviated as VTR), optical disk or other recording medium for subsequent reproduction and use. Many of such data, pictures and voices are desirably concealed from third persons. In order to secure such information, a scramble encoder is generally employed. However, the conventional scramble encoders demand a large-scale encoding system and encoder and do not allow us to secure information in an easy manner. Thus, there has not been available a device by which confidential information could be conveniently recorded on VTR, for instance, and the recorded information be easily reproduced with security retained and this has been an obstacle to the transmission of confidential data and information.
Presented in FIG. 8 is a block diagram showing the basic construction of the conventional scramble encoder. As shown, the reference numeral 101 represents a computer (hereinafter abbreviated as CPU) which controls the entire scramble encoder. Depending on the system scale, a variety of CPUs from a personal computer to a large universal computer are employed. The picture signal and sound signal are applied to a picture scrambler 102, which scrambles the picture signal, and a sound scrambler 103, which scrambles the sound signal, respectively. A key signal generating circuit 104 generates a key signal which is synchronized with the picture signal. A superimposing circuit 105 superimposes this key signal on the picture signal scrambled by the picture scrambler 102. The sound signal is FM-modulated by an FM modulating circuit 106 and a mixing circuit 107 mixes it with the scrambled picture signal to provide a scrambled composite video signal.
The principle of operation of a scramble encoder is now explained. While many systems can be contemplated and used for the picture scrambler 102, a scrambling technology which is known as line rotation in which the picture signal scan line is cyclically shifted is explained here. This line rotation processing comprises setting a cutting point for shifting the picture signal scan line at x on the CPU 1, coding this cutting point x using the key signal (Kj) and forming this coded X into a binary signal in the key signal forming circuit within the vertical retrace period. For scrambling the sound signal, the sound signal is A/D converted and encoded by adding a pseudorandom signal (hereinafter abbreviated as PN signal). And only the initial value of this PN signal is superimposed and transmitted.
At the receiving end which received the above signal, the signal can be descrambled by executing the reverse of the encoding procedure. Taking the descrambling of the sound signal as an example, the initial value of PN is applied to a PN generating circuit to generate a PN signal series for descrambling and a demodulation to the original signal is performed according to this PN signal series. For the descrambling of the picture signal, the read position (corresponding to the cutting point in scrambling) is logically determined from the initial value of PN transmitted every field or in a predetermined cycle. The algorithm for the above determination procedure is not disclosed for enhanced security.
However, since the conventional scramble encoder and encoder are bulky and costly, they could not be easily built into the television receiver and the home VTR. Therefore, only the descrambler was miniaturized and used as connected to the television receiver. However, this requires an additional space and an additional expenditure.